The invention relates to a fuel metering system for internal combustion engines, comprising a fuel reservoir and a fuel line leading from the fuel reservoir to a suction tube. The fuel line has within it a location with controllable cross section. The metering system further comprises an air line, also controllable in cross section. The fuel quantity metered out to the air quantity streaming through the suction tube is adjustable in dependence on the pressures prevailing in the fuel reservoir and in the suction tube as well as on the output signal of a measuring probe which determines the composition of the exhaust gas.
The purpose of such a fuel metering system is to automatically provide a favorable fuel-air mixture ratio for an Otto engine under all operational conditions in order to burn the fuel as completely as possible and therefore to avoid or to reduce sharply the generation of toxic exhaust gases while maintaining the highest possible performance and the lowest possible fuel comsumption of the internal combustion engine.
For this purpose it is required that during the start-up of a cold engine and during the warm-up phase of that engine, the fuel air mixture be richer than is required for a warm engine, i.e. the fuel portion must be greater. But even with a warm engine, the fuel quantity must be metered very precisely depending on the requirements of each operational condition of the internal combustion engine. In particular, the proportionality between air quantity and fuel quantity must be changeable in dependence on the engine parameters.
In known fuel metering systems of this kind, the output signals of the measuring probe which exhibit voltage fluctuations are integrated in electronic circuitry and serve as an integrated voltage in the generation of the control value for changing the pressure in the suction tube or in the fuel reservoir.